Myxococcus xanthus is a bacterium which undergoes a simple cycle of multicellular development. It is an attractive and experimentally tractable system in which to study the role of cell-cell interactions in the regulation of gene expression. The obligatory involvement of intercellular communication during its development is implicated by the behavior of several non-developmental mutants. The research described in this proposal will focus on one group of mutants which fail to produce an intercellular signal required completion of the final stages of the developmental program. The objective of this study is to understand the nature of this interaction and the mechanism by which it modifies gene expression. Classical genetics will be augmented by gene fusion and recombinant DNA technoloty to identify specific genes whose expression is modulated by perception of the signal, to identify the apparatus which perceives the signal and the mechanism by which the signal exerts its effect on gene expression. The long range goal of this research is to understand the means by which this organism coordinates the activities of individual cells during multicellular activities, and to understand in molecular detail the channels through which this form of communication flows. This information may help to provide a framework for thinking about more complex tissue interactions. In this way it is hoped that this work may help us to understand situations in which intercellular coordination goes awry -- situations which may in part lead to tragedies such as birth defects and malignancies.